Optical elements such as optical lenses have long been used to manipulate light for various advantages. Recently, micro-diffraction gratings have been utilized in holographic and augmented/virtual reality (AR and VR) devices. One particular AR and VR device is a wearable display system, such as a headset, arranged to display an image within a short distance from a human eye. Such wearable headsets are sometimes referred to as head mounted displays, and are provided with a frame displaying an image within a few centimeters of the user's eyes. The image can be a computer-generated image on a display, such as a micro display. The optical components are arranged to transport light of the desired image, where the light is generated on the display to the user's eye to make the image visible to the user. The display where the image is generated can form part of a light engine, so the image generates collimated light beams guided by the optical component to provide an image visible to the user.
Different kinds of optical components have been used to convey the image from the display to the human eye. To properly function in an augmented reality lens or combiner, the geometries of an optical grating may be designed to achieve various effects. In some devices, multiple different regions, such as two or more different regions, are formed on the surface of a lens, wherein the grating geometries in one region are different from the grating geometries in other regions.
Angled surface relief optical gratings can be produced by the direct etching of angled trenches into a substrate or a film stack on a substrate. One of the parameters controlling the efficiency of the optical grating is the trench depth. Unfortunately, current approaches of forming optical gratings with varied heights, widths, and/or shapes across diffracting and viewing fields have proved challenging.
Therefore, there is a need for improved methods of producing gratings having trenches with variable height and width.